This invention relates to cooling systems and more particularly to a cooling system for use in cooling electronic components. Even more particularly, this invention relates to a cooling system for cooling electronic printed circuit cards which are mounted in a rack, or card cage.
In any electronic or electro-mechanical device where the electronic circuitry is mounted on printed circuit cards which are organized so that they may be installed in a rack, or card cage, appreciable heat is generated, and this heat must be transferred away from the printed circuit cards or it will destroy or seriously damage them. Normally the printed circuit cards are cooled by air flow provided by fans or the like. In order to maintain this equipment, access is needed to the printed circuit cards so that they may be removed and replaced and so that test equipment may be attached to the cards to test the circuits. In modern electronic devices, the card cage typically is mounted inside the device during normal operation and must be transferred outside the device for maintenance. While outside the device during maintenance, the device must still be capable of operating, thus the printed circuit cards must be cooled by air flow, just as they are cooled when the card cage is inside the device.
In the prior art, mechanisms for cooling printed circuit cards which allow the card cage to move are of two general types: those which provide cooling air to the card cage by means of a hose connected to a central air supply, and those which mount cooling fans directly to the bottom of the card cage. Each of these mechanisms has certain strong points and weak points, as discussed below. An important advantage of the present invention is that it overcomes all the disadvantages of the prior art, while retaining all the advantages of both of the prior art mechanisms.
The hose mechanism has the advantage that air is supplied by one central fan motor which reduces cost both in the motor and in providing noise reduction. It is also less expensive to monitor the operation of this one fan and shut down the device if the fan motor should fail. Since the air always passes this fan, the air can be filtered at this point, thus only one filter is needed to ensure that the air is free of contaminating particles. The disadvantage to this system is that a flexible air hose is needed to connect the central air supply to the card cage. This hose adds cost to the device and increases maintenance. If the card cage is not moved from the maintenance position to the normal operating position carefully, the hose can become pinched, and the air supply to the card cage will be reduced or shut off causing the components to eventually fail. To provide sufficient air, this hose must be large and bulky. Providing space for this bulky hose increases the overall size and cost of the device.
By mounting fans directly to the bottom of the card cage, the hose can be eliminated. In many systems, however, the card cage is large enough to require several fans, thus increasing the overall cost of the device. Increasing the number of fans also increases the failure rate. Extra electrical wiring must be provided to the fans, extra noise reduction material must be added, and normally, an air filter must be provided for each fan.
The advantage of the present invention over the prior art is that it allows for a central air supply, thus reducing cost and maintenance, while it does not require a hose to connect this air supply to the card cage.